Tortorelli, Susanna (2011) On the flexural performance of steel beams. [Tesi di dottorato] (Unpublished)

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In this thesis are presented results of different kind of investigation about both monotonic and cyclic behaviour of steel beams. With the aim to quantify the rotation capacity and flexural overstrength of steel beams an experimental activity was performed in the Civil Engineering Laboratory at the University of Salerno in the framework of ReLUIS project. At the light of the experimental results, and with the aim to continue the study on the behaviour of steel beams avoiding additional expensive experimental campaigns, finite element models has been used to perform numerical simulations (in Abaqus 6.10) of the experimental tests actually carried out. The numerical results have been compared with the experimental ones to demonstrate the validity of the assumptions made in the modelling phase, with positive response. Then, a wide parametrical analysis, carried out by means of finite element simulations, has been performed, on the basis of the previous calibration of the numerical models. In this way, the obtained results goes to enlarge the existing database of results, to be able, in the end, to propose a new empirical formulation for the parameters “R” and “s” in case of monotonic loads. The proposed equations are obtained from a multiple linear regression of experimental and numerical data on monotonic tests, from literature and from the work carried out for this thesis. It was observed that interaction between web and compression flange slenderness could limit the rotation capacity of flexural members. This interaction can lead to reduced inelastic deformation capacity, measured as rotation capacity, when either the web or the compression flange slenderness is too large. So, steel beam classification can be considered outdated, due to the fact that the rotation capacity “R” and the flexural overstrength “s” can be properly calculated by means of the tools provided by this work. The correct value of the flexural overstrength “s”, as calculated with the new proposed formulation, can be properly used for the application of the capacity design criteria. An analogous parametric analysis has been performed for cyclic loading pattern, demonstrating that the experimental and numerical results indicated that the loading condition has a significant influence on rotation capacity. In particular, it decreased when the loading is cyclic, and cyclic rotation capacity “R” can be estimated as about 30% of monotonic “R”. So, for seismic application, it is auspicable the use of the cyclic rotation capacity “R”, and not the monotonic one. These critical considerations on the differences between the monotonic and the cyclic behaviours that were made, in future can be used to go beyond the final scope of this thesis. In particular it can be used to start a study to establish a connection between seismic demand and seismic capacity of steel beams. In particular, for seismic design it will be necessary to correlate cyclic “R” and behaviour factor “q” for steel structures.

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